Amplifier



J. P. BARTON May 15, 1934.

AMPLIFIER 2 Sheets-Sheet 1 Filed July 18 1930 IN'VENTOR James. P Barton.

ATTO'RNEY May 15, 1934. BARTON 1,958,881

AMPLIFIER Filed July 18, 1930 2 Sheets-Sheet 2 INVENTOR BY I ATTOiRNEY James P. Barron.

Patented May 15, 1934 UNHTE STATES T QFFIC AIWPLIFIER Application July 18, 1930, Serial No. 468,856

4 Claims.

My invention relates to radio circuits, more particularly to circuits embodying oscillation generators and means for coupling the genera tors to an amplifying circuit. 5 Devices and systems of this character, according to the teachings of the prior art with which I am familiar, possess certain inherent disadvantages and defects. In superheterodyne receivers, particularly those wherein an oscilla- 0 tion generator is provided to produce oscillatory currents or potentials to beat with incoming signals, difliculty has been experienced. An oscillation generator, according to prior art, is normally coupled to the receiving circuit, more specifically, the first detector stage, by an inductive or capacitative coupling. The amplitude of the generated oscillatory current or potential, as introduced into the detector circuit, is controlled for volume-control purposes, either by Varying or adjusting the inductive or capacitative coupling between the oscillator and the detector or it may be accomplished by a variable resistance in the filament circuit of the oscillator, whereby the potential at the filament may be altered to obtain the desired results.

In circuits utilizing a variable inductive or capacitative coupling, changes in degree of coupling produce reactive effects in the circuits to alter the frequency of the system, whereby it becomes necessary to retune the system to obtain the point of maximum reception each time the coupling is altered.

Where filament-control means is utilized, other disadvantages become apparent. Particularly, when feeding a filament through a balanced circuit from an alternating-current source, it has been found that a thermionic device functions with a minimum amount of hum at one point on its operating curve. If the filament potential has to be varied to obtain a change in the amplitude of an oscillatory current or potential, the operation of the thermionic device will be shifted from this point of least hum and it will become apparent that this will result in an increase in the hum of a receiver. In addition to the above, it will also be obvious that thermionic devices may be caused to operate at an efliciency, lower than the normal operating efiiciency which, from an economical viewpoint, is undesirable. Furthermore, the operation of a variable resistor. in the filament circuit, as a volumecontrol means, is productive of noise and is nonuniform in its action.

My invention has for one of its objects to provide a circuit of the type described which shall be substantially free from the disadvantages and defects of prior circuits, as described above.

Another object of my invention is to provide volume-control means which shall be smooth in action, and uniformly quiet in operation.

Another object of my invention is to provide means for coupling an oscillator to a circuit, wherein the coupling for any particular setting will remain constant and independent of the frequency of the circuit.

Additional objects of my invention will be apparent from the following description, taken in conjunction with the accompanying drawings wherein I have disclosed, in Fig. 1 thereof, a circuit diagram of one embodiment of my invention.

In Figs. 2, 3 and 4, I have disclosed, in circuit diagrams, modifications of the invention, as illustrated in Fig. 1. I

Broadly speaking, my invention comprises an oscillation generator coupled to a radio circuit and means for varying the amplitude of the oscillations for providing volume-control in the circuit.

Referring more particularly to Fig. 1 of the drawings, the apparatus shown therein comprises a circuit diagram of a superheterodyne receiving circuit. Since my invention resides in specific improvements in the above circuit, I have disclosed the portions of a circuit not involved in my improvements in simplified form, for the purpose of explanation.

Briefly speaking, therefore, the system disclosed comprises a stage of radio-frequency amplification 1 coupled to an antenna circuit 3. The output of the radio frequency amplifier is passed on through the first detector stage 5 and thence amplified through a stage of intermediate-frequency amplification 7, the output circuit of which is coupled to a second detector, 9, where the signal is detected a second time, and the intermediate frequency is converted into signals at audio frequency. These signals are then amplified, through a stage of audio-frequency amplification 11, in the plate circuit of which is an energy-translating device 13 capable of being operated by the amplified audio-frequency currents.

Normally coupled to the first detector stage is an oscillation generator 15 for the purpose of 10., generating oscillatory currents or potentials which may be utilized in heating with the radiofrequency signals in the first detector stage to produce signals at intermediate frequencies in the output circuit of the detector.

Potentials for the various thermionic devices utilized in the circuit are derived from a voltage divider 17 which is normally bridged across the output terminals of a socket power unit (not shown).

My invention relates particularly to the oscillation generator and its association with the first detector stage.

The first detector 5 comprises a thermionic device having a grid circuit 19 and a plate circuit 21 associated therewith. In the cathode lead, which is common to both circuits, I provide a pair of serially connected resistors 23 and 25 which normally serve the purpose of providing grid bias for the grid 27 of the thermionic device for optimum detection, the amount of grid bias being determined by the potential drop across the resistors, as caused by the plate current flowing through the resistors. A small capacity 24, shunting the upper resistor 23, provides a by-pass for high-frequency currents.

While I have disclosed the detector as utilizing plate detection, my invention may be used with a detector utilizing grid-leak detection, with equally good results.

The oscillation generator 15 also comprises a thermionic device having a grid circuit and a plate circuit associated therewith, the grid circuit comprising a blocking condenser 29 shunted by a high resistance 31 and an input coil '33 connected to the cathode 35 of the tube and ground 37 through a resistor 39.

The plate circuit comprises a blocking condenser 41 and a coil 43 connected to the cathode 35 and ground 37 through the same resistor 39,

' both coils 33 and 43 being shunted by a variable 1 coupling arrangement may be traced from ground connection 37, through the resistor 25, the conductor 4'7 and the oscillation generator resistor 39, back to ground.

The oscillator described above is of the Hartley type, but my invention is not necessarily limited to the use of a Hartley oscillator, as it is equally adaptable for use in combination with any oscillator.

The particular values of the resistors referred to may be varied within wide limits, but, in my preferred embodiment, the resistor 39 in the oscillation generator should be of such value that the alternating-current voltage across it is sufiicient to modulate properly the signal in the detector-grid circuit. The resistor 25 in the detector stage may be from 4 to 10 times as large as the resistor 39 of the generator. The resistor 25 may, for example, have a resistance anywhere in the neighborhood of 2000 to 4000 ohms, when used in conjunction with tubes of the UK 227 type.

From a study of the circuit, it will be apparent that the potential across the lower resistor 25 in the detector stage will be equivalent to the potential drop across that portion of the oscillation-generator resistor which is included between the variable contactor 49 and ground connection 37. Variations of the contact along the resistor 39 will increase or decrease the amplitude of the current transferred from the oscillator to the detector stage. As the contact is moved toward the grounded end, the potential or current amplitude will decrease and approach and substantially reach zero value, which would be the equivalent of lowering the potential across the resistor 25 in the detector stage.

As a result of the variations in the amplitude of the oscillatory current or potential impressed on the detector stage, a corresponding change will be produced in the amplitude of the beatfrequency currents or potentials produced therein, the effect of which will be to change the degree of potential variations on the grid of the detector tube and so produce a shift in the volume level of the system.

This system, therefore, will provide excellent volume-control means for the receiving circuit disclosed. Since the action of the oscillator is neither affected nor interfered with, as is the case when inductive or capacitative coupling is used or when filament control is resorted to, to vary current or potential amplitude, it will be apparent that no reactions will be set up between the oscillator and the detector. For any particular value or setting of the variable contact, the degree of coupling will remain constant, and the operation of the device will be uniform. The volume control, as obtained by manipulating the contact 49, will be smooth in action and quiet in operation.

In addition to the above, in my particular arrangement, one side of the coupling circuit is maintained at ground potential, which is very desirable from the view-point of stable operation.

The modifications of my invention, as disclosed in Figs. 2 to 4 inclusive bear close resemblance to the embodiment shown in Fig. 1. Only the relevant portions of the system disclosed in Fig. l are illustrated, and elements common to all the modifications bear the same reference numerals.

Referring more particularly to Fig. 2, I have shown my invention as applied to the first detector stage of a system incorporating means for neutralizing feedback. The specific neutralizing means best adapted for operation with this particular modification being the Rice neutralization circuit, although other similar neutralizing schemes may be used. In this species, the common resistor or impedance-coupling element 25 is connected in the input circuit of the first detector, preferably in the lead from a point intermediate the extremities of the input coil to maintain symmetry in this coil with the preceding radio-frequency transformed to the cathode which is grounded. Connection to the oscillator is provided for by means of a conductor 47 ex tending from the ungrounded end of the resistor 25 to the variable resistor 39 of the oscillator. A condenser 51 may be inserted in the conductor 47 to separate the alternating-current and direct-current components existing in the resistor 39 and thus permit only the alternating component to be impressed upon the detector circuit.

By inserting the impedance-coupling element 25 in the grid circuit only as shown, the detector plate current can no longer flow through it, as in the species of Fig. 1 and, consequently, the possibility of the detector bias being disturbed is avoided.

In Fig. 3, the modification embodied therein, is s m lar to that of Fig. 2 except that the un grounded end of the resistor 25, instead of being connected to an intermediate point on the input coil, as when using Rice neutralization means in the system, is connected to the low-potential end of the coil. The operation of the invention will be substantially the same, the connection disclosed in Fig. 3 being adaptable for use in combination With other neutralizing schemes.

Referring to Fig. 4, the modification disclosed therein comprises a radio-frequency choke-coil 53 in series with the grid-bias element 23, both being connected in the cathode lead to ground. the function of this particular arrangement is to maintain, in a separate state, the current flowing in the plate circuit of the detector and the oscillatory current impressed on the input circuit of the detector.

Since the impedance of the resistor 39 is materially less than the impedance of the resistor 23 and choke-coil 53, any oscillatory current flowing in the grid circuit of the detector will favor the path through the resistor 39, or, more accurately stated, through that portion of the resistor 39 located between the variable contact 49 and the grounded end. The detector-plate current, on the other hand, being a direct current, will be blocked by the condenser 51 and, therefore, it will favor the path through the resistor 23 and choke-coil 53 instead of the resister 39. The operation of the circuit to vary the amplitude of the oscillatory current or potential impressed on the detector circuit, thereby to change the volume level of the system, is basically the same as that of the other species or modifications disclosed and explained above. In lieu of the serially connected resistance and choke-coil, I might use a choke-coil having the required amount of resistance.

Since, under certain conditions of operation, depending upon the value of grid bias on the detector tube, only potentials will be impressed upon the input circuit of the detector stage from the oscillation generator, I have used the terms oscillatory current and oscillatory potential interchangeably throughout the description and refer to them generically as an electrical oscillatory condition.

Although I have disclosed my coupling elements as comprising resistors, it may be desirable, nnder certain conditions, to utilize, in lieu thereof, capacitances or inductances.

Various other modifications may suggest themselves within the scope of my invention, which is not necessarily limited to the system described but may be adapted to any circuit.

Therefore, I do not desire to be limited to the details described above, except insofar as is necessitated by the prior art and the scope of the appended claims.

I claim as my invention:

1. In a system of the radio type, a signal receiving circuit, an oscillation generator comprising an electric discharge device having a cathode, an impedance so connected in the lead to said cathode as to have a potential of the generator frequency developed thereacross, and means electrically coupling said impedance with said signal receiving circuit.

2. In a system of the radio type, an electron discharge device, a circuit connected thereto including a resonant circuit, an oscillation generator also having a resonant circuit and an electrical path connecting portions of said generator and said electron discharge tube circuit independently of said resonant circuits, said path and connected portions constituting the sole path for the transfer of energy between said oscillation generator and said electron discharge tube circuit.

3. In a system of the radio type, a signal receiving circuit having a resonant circuit, an oscillation generator also having a resonant circuit and means electrically coupling said oscillation generator with said signal receiving means independently of said resonant circuits for the transfer of energy from said generator to said signal receiving means, said means including an impedance so located in said oscillation generator as to have a potential of the generator frequency developed thereacross.

4. In a system of the radio type, an electron discharge device having a circuit including a resonant circuit, an oscillation generator also having a resonant circuit and means electrically coupling said oscillation generator with said signal receiving means independently of said resonant circuits for the transfer of energy from said generator to said signal receiving means, said coupling means including an impedance so located in said generator circuit as to have a potential of the generator frequency developed thereacross.

JAMES P. BARTON. 

